This invention relates to joined ceramic and metal having high strength.
A known method for joining ceramic and metal is metallic activation, in which solder is inserted between ceramic and metal, heated, then melted to join ceramic and metal. An alloy containing activated metal, such as silver-copper-titanium alloy (referred to as Ag-Cu-Ti alloy) or silver-copper-nickel-titanium alloy (Ag Cu-Ni-Ti alloy), is widely used as the solder. The solder can easily join ceramic and metal in low temperature range between 800.degree. C. and 900.degree. C. with high joining strength
For another metallic activation, Japan Published Examined Patent Application 35-1216 and Japan Published Unexamined Patent Application 61-127674 disclose ceramic and metal joined through an intermediate solder member which is a combination of titanium (Ti) and an eutectic metal element such as nickel-titanium (Ni-Ti) alloy, nickel copper-titanium (Ni-Cu-Ti) alloy, or copper-titanium (Cu-Ti) alloy.
The intermediate solder member should strengthen the joining of ceramic and metal, but in the Ag-Cu-Ti alloy and the Ag-Cu-Ni-Ti alloy, the eutectic point of Ag-Cu alloy is as low as 780.degree. C., and Cu is selectively oxidized. Accordingly, such an intermediate solder member cannot assure adequate joining strength at high temperature.
The Ni-Ti alloy, the Ni-Cu-Ti alloy, and the Cu-Ti alloy assure almost the same joining strength at high temperature as that at low temperature, but have the joining strength lower than that of Ag-Cu alloy due to their low wettability. Accordingly, the Ni-Ti, Ni-Cu Ti, and Cu-Ti alloys are unreliable, require a long time period for heat treatment, and are expensive to manufacture.